| Message ID | 1308753606-17928-1-git-send-email-peter.maydell@linaro.org |
|---|---|
| State | New |
| Headers | show |
Ping? On 22 June 2011 15:40, Peter Maydell <peter.maydell@linaro.org> wrote: > Expand the note on the number of TCG ops generated per target insn, > to be clearer about the range of applicability of the 20 op rule > of thumb. Also add a note about the hard MAX_OP_PER_INSTR limit. > > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> > --- > The expansion of the first bullet point is based on remarks by > Aurelien in this email: > http://lists.gnu.org/archive/html/qemu-devel/2011-06/msg00395.html > > tcg/README | 10 +++++++++- > 1 files changed, 9 insertions(+), 1 deletions(-) > > diff --git a/tcg/README b/tcg/README > index 6600122..cfdfd96 100644 > --- a/tcg/README > +++ b/tcg/README > @@ -504,7 +504,15 @@ register. > - Don't hesitate to use helpers for complicated or seldom used target > instructions. There is little performance advantage in using TCG to > implement target instructions taking more than about twenty TCG > - instructions. > + instructions. Note that this rule of thumb is more applicable to > + helpers doing complex logic or arithmetic, where the C compiler has > + scope to do a good job of optimisation; it is less relevant where > + the instruction is mostly doing loads and stores, and in those cases > + inline TCG may still be faster for longer sequences. > + > +- The hard limit on the number of TCG instructions you can generate > + per target instruction is set by MAX_OP_PER_INSTR in exec-all.h -- > + you cannot exceed this without risking a buffer overrun. > > - Use the 'discard' instruction if you know that TCG won't be able to > prove that a given global is "dead" at a given program point. The > -- > 1.7.1 > > >
Thanks, applied. On Wed, Jul 13, 2011 at 2:00 PM, Peter Maydell <peter.maydell@linaro.org> wrote: > Ping? > > On 22 June 2011 15:40, Peter Maydell <peter.maydell@linaro.org> wrote: >> Expand the note on the number of TCG ops generated per target insn, >> to be clearer about the range of applicability of the 20 op rule >> of thumb. Also add a note about the hard MAX_OP_PER_INSTR limit. >> >> Signed-off-by: Peter Maydell <peter.maydell@linaro.org> >> --- >> The expansion of the first bullet point is based on remarks by >> Aurelien in this email: >> http://lists.gnu.org/archive/html/qemu-devel/2011-06/msg00395.html >> >> tcg/README | 10 +++++++++- >> 1 files changed, 9 insertions(+), 1 deletions(-) >> >> diff --git a/tcg/README b/tcg/README >> index 6600122..cfdfd96 100644 >> --- a/tcg/README >> +++ b/tcg/README >> @@ -504,7 +504,15 @@ register. >> - Don't hesitate to use helpers for complicated or seldom used target >> instructions. There is little performance advantage in using TCG to >> implement target instructions taking more than about twenty TCG >> - instructions. >> + instructions. Note that this rule of thumb is more applicable to >> + helpers doing complex logic or arithmetic, where the C compiler has >> + scope to do a good job of optimisation; it is less relevant where >> + the instruction is mostly doing loads and stores, and in those cases >> + inline TCG may still be faster for longer sequences. >> + >> +- The hard limit on the number of TCG instructions you can generate >> + per target instruction is set by MAX_OP_PER_INSTR in exec-all.h -- >> + you cannot exceed this without risking a buffer overrun. >> >> - Use the 'discard' instruction if you know that TCG won't be able to >> prove that a given global is "dead" at a given program point. The >> -- >> 1.7.1 >> >> >> > > > > -- > 12345678901234567890123456789012345678901234567890123456789012345678901234567890 > 1 2 3 4 5 6 7 8 > >
diff --git a/tcg/README b/tcg/README index 6600122..cfdfd96 100644 --- a/tcg/README +++ b/tcg/README @@ -504,7 +504,15 @@ register. - Don't hesitate to use helpers for complicated or seldom used target instructions. There is little performance advantage in using TCG to implement target instructions taking more than about twenty TCG - instructions. + instructions. Note that this rule of thumb is more applicable to + helpers doing complex logic or arithmetic, where the C compiler has + scope to do a good job of optimisation; it is less relevant where + the instruction is mostly doing loads and stores, and in those cases + inline TCG may still be faster for longer sequences. + +- The hard limit on the number of TCG instructions you can generate + per target instruction is set by MAX_OP_PER_INSTR in exec-all.h -- + you cannot exceed this without risking a buffer overrun. - Use the 'discard' instruction if you know that TCG won't be able to prove that a given global is "dead" at a given program point. The
Expand the note on the number of TCG ops generated per target insn, to be clearer about the range of applicability of the 20 op rule of thumb. Also add a note about the hard MAX_OP_PER_INSTR limit. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- The expansion of the first bullet point is based on remarks by Aurelien in this email: http://lists.gnu.org/archive/html/qemu-devel/2011-06/msg00395.html tcg/README | 10 +++++++++- 1 files changed, 9 insertions(+), 1 deletions(-)